1. Field of the Invention
The present invention relates to lithography technology, more particularly, to a method for patterning a photoresist film using a lithographic process.
2. Description of the Related Art
Due to the recent high growth of information and communication technologies, the technology of manufacturing semiconductor devices has rapidly developed. A semiconductor device has been developed toward higher integration, miniatuarization, and higher operational speed. Also, the requirements on microlithography for improving a degree of integration has become severe.
Lithography technology is used to transfer patterns formed on a mask to a layer of radiation-sensitive material covering the surface of a substrate, and is a core technology used to provide a high degree of integration and minuteness in semiconductor devices. Generally, a lithographic process is carried out through a sequence of processes including a coating process of a photoresist film, a soft bake process, an alignment process, an exposure process, a post exposure bake (PEB) process, and a development process.
A photoresist has a photosensitivity to light, and has a resistance against the etching of underlying layers. Photoresist material is divided into a positive photoresist, and a negative photoresist. The positive photoresist, having a high resolution and superior resistance against etching, is widely used in a high integration semiconductor process, wherein reactions such as decomposition, scission of molecular chains, and so on, occur so that the solubility is greatly increased in a portion exposed to a light which is removed during the development process. By comparison, in the negative photoresist, a crosslinking reaction occurs so that the molecular weight is greatly increased in a portion exposed to light, and the exposed portion becomes insoluble in the development solution. After development, the unexposed portion is expunged.
A development process is the process in which a photoresist that was changed by exposure to light is removed so as to transfer a pattern of a mask into a substrate. It is generally used in a wet development process with an alkaline aqueous solution developer containing Tetra Methyl Ammonium Hydroxide (TMAH) as a main component.
There are several methods of development, such as a puddle method, a spray method, and a dipping method. In a puddle method, a photoresist film is developed in a state in which a substrate is has moved after applying a developer. In a spray method, a developer is continuously sprayed during a development process. The spray method is advantageous in successive processes, but the developer is extremely exhausted. A dipping method may not be available for successive processes.
In any one of these method of development, problems such as scum, and photoresist residues disturb the etching of an underlying layer during an etching process, and form a bridge between wiring lines which causes a short failure of a device.
FIG. 1 is a cross-sectional view illustrating scums and photoresist residues. The photoresist pattern is formed by developing a photoresist film 12, after aligning and exposing a photoresist film 12 coated on an underlying layer 11 of a semiconductor substrate 10. Scum 12a and photoresist residues 12b, due to incomplete removal of a photoresist film 12, are causes of failures in succeeding processes. Especially, in pad opening processes for opening metal pads to be bonded to external circuits, relatively thick photoresist film and low exposure energy are used so that failures frequently take place such as scum due to nonuniformity of the thickness of photoresist film and nonuniformity of the exposure energy.
In case an underlying layer 11 is formed of silicon oxynitride such as SiON, or silicon nitride such as SiNx, a photo acid generator of the photoresist reacts with the silicon oxynitride or silicon nitride. As a result, a new resultant material is formed. This resultant material has such a low reactivity with the developer that it frequently remains in the form of scum without being removed in the developing process. Since an underlying layer is generally formed of silicon nitride in such pad opening processes, the problem of scum takes place more frequently.
Hereinafter, a lithography process will be explained including a related art method of patterning a photoresist film, with reference to FIG. 2 illustrating a flow chart of a related art lithography process.
First, after a surface treatment is carried out in order to reinforce an adhesive strength of a photoresist, a photoresist film is coated (S100). In order to reinforce an adhesive strength, the material which makes the surface of a substrate hydrophobic so as to improve resistance against water, for example HMDS (Hexa Methyldisilazane), is put in a tank with nitrogen gas and coated on the substrate in vapor.
Next, a soft bake process and an exposure process are carried out, after a mask is aligned on the substrate (S101). A soft bake process is used to remove a photoresist solution and set up on temperature condition for components of photoresist not to be pyrolyzed.
Next, PEB and development processes are carried out (S102). The PEB is carried out to improve uniformity of critical dimension within the substrate by preventing a standing wave phenomenon. At this moment, scum, photoresist residue and so on take place after a development process.
Finally, the photoresist film is removed after a desired pattern is obtained by etching the underlying layer (S103). The problems such as scum, photoresist residues, and so on, disturb the etching of the underlying layer, thus forming a bridge between wiring lines which causes a short failure of a device.
To resolve the above described problem, Korean patent laid-open publication No. 2003-0056342 describes a method for forming a pattern in semiconductor device, including steps of forming thin film to be desired to form into a pattern, carrying out a surface treatment at the thin film using O2 plasma, and forming a photoresist pattern on the thin film which the plasma process is carried out. However, such a method has limitations in properties of a thin film, and problems that it is impossible to remove scum occurring even after a plasma process.